1. Field of the Invention
The present invention relates to recordable information storage media, and more particularly, to an information storage medium designed to control optimum writing power in optimal power control (OPC) areas even when eccentricity occurs among a plurality of information storage layers and a method and apparatus for recording/reproducing data on/from the information storage media.
2. Description of the Related Art
General information storage media are widely used as information recording media of optical pickup apparatuses for recording/reproducing data in a non-contact way. Optical disks are used as the information storage medium and are classified as compact disks (CDs) or digital versatile disks (DVDs) according to their information storage capacity. Examples of recordable, erasable, and reproducible optical disks are 650 MB CD-R, CD-RW, 4.7 GB DVD+RW, and the like. Furthermore, HD-DVDs having a recording capacity of 25 GB or greater are under development.
As described above, information storage media have been developed to have a greater recording capacity. The recording capacity of an information storage medium can be increased in two representative ways by: 1) reducing the wavelength of a recording beam emitted from a light source; and 2) increasing the numerical aperture of an objective lens. In addition, there is another method of forming a plurality of information storage layers.
FIG. 1 schematically shows a dual-layered information storage medium having first and second information storage layers L0 and L1. The first and second information storage layers L0 and L1 include first and second optimal power control (OPC) areas 10L0 and 10L1, respectively, for obtaining an optimal writing power and first and second defect management area (DMAs) 13L0 and 13L1, respectively. The first and second OPC areas 10L0 and 10L1 are disposed to face each other.
Data is recorded in the first and second OPC areas 10L0 and 10L1 using various levels of writing power to find the optimum writing power. Hence, data may be recorded at a power level higher than the optimum writing power. Table 1 shows variations in the jitter characteristics of each of the first and second information storage layers L0 and L1 when data is recorded in the OPC areas with different levels of writing power.
TABLE 1Writing power about 20%higher than normal writingNormal writing powerpowerL0WritingUnwrittenWritingWrittenWritingWrittenL1UnwrittenWritingWrittenWritingWrittenWritingJitterL05.9%6.0%5.8%5.9%->6.4%L16.3%6.2%6.3%6.2%->6.3%WritingL06.46.36.37.56.4PowerL16.06.06.26.07.2
According to Table 1, if data is recorded with normal writing power, the jitter characteristics of the first or second information storage layer L0 or L1 remain constant. On the other hand, if data is recorded with writing power about 20% higher than the normal writing power, the jitter characteristics of the OPC area of a first or second information storage layer L0 or L1 in which data has already been recorded are degraded. If data is recorded on one of the first and second information storage layers L0 and L1 with writing power more than 20% higher than the normal writing power, it can be expected that the jitter characteristics of the other information storage layer may be further degraded.
Hence, if the first and second OPC areas 10L0 and 10L1 of the first and second information storage layers L0 and L1 exist within an equal radius as shown in FIG. 1, one of them may not be usable.
The recording status of one of the first and second OPC areas 10L0 and 10L1 may affect the recording characteristics of the other OPC area. For example, as shown in FIG. 2A, if data has been recorded on a part 10L0_A of the first OPC area 10L0 and no data has been recorded on the residual area 10L0_B thereof, the recording property of a part of the second OPC area 10L1 which corresponds to the occupied part 10L0_A of the first OPC area 10L0 is different from that of a part of the second OPC area 10L1 which corresponds to the unoccupied part 10L0_B of the first OPC area 10L0. In other words, since the transmittance of the laser with respect to the occupied part 10L0_A of the first OPC area 10L0 is different from the transmittance of a laser with respect to the unoccupied part 10L0_B thereof, the recording property of the second OPC area 10L1 may be irregular over the area.
As described above, if the first and second OPC areas are disposed within an equal radius, they may not properly function.
During the manufacture of an information storage medium, eccentricity may occur. For example, an information storage medium having a single information storage layer may have eccentricity of about 70-80 μm(p-p) (where p denotes a peak). To manufacture an information storage medium having first and second information storage layers L0 and L1, the first and second storage layers L0 and L1 are separately manufactured and then attached to each other. When eccentricity occurs during the manufacture of each of the first and second information storage layers L0 and L1, they may be attached to each other such that areas of the first information storage layer L0 are not aligned with those of the second information storage layer L1 as shown in FIG. 2B.
When the first and second OPC areas 10L0 and 10L1 are not in line, overlapped areas generated due to the out-of-line arrangement may affect each other. For example, if data is recorded on the first OPC area OPC_L0 using higher power than the normal writing power, the first OPC area OPC_L0 adversely affects a defect management area (DMA_L1) of the second information storage layer L1 because the DMA_L1 contacts a part C of the first OPC area 10L0. Also, a part D of the second OPC area OPC_L1 may adversely affect a part of the first information storage layer that contacts the part D, and thus the part may not be used.